Hopes were high when the Mars Climate Orbiter launched from Cape Canaveral on December 11, 1998. The robotic space probe was designed to study the climate, atmosphere, and surface changes of Mars and to act as a communications relay for the Mars Polar Lander.

For the next ten months, all went according to plan as the Orbiter sped to the Red Planet. On September 23, 1999 the Orbiter began its orbital insertion maneuver exactly on schedule. Four minutes later NASA lost contact with the spacecraft — never to regain communications.

What caused this $125 million failure? Was it alien incursion? Industrial sabotage? An uncharted quantum singularity?

Actually, it was the metric system — at least, according to Lockheed Martin, the supplier of a vital piece of software. Of course, if you ask NASA and the Jet Propulsion Laboratory (JPL), they would say the problem was the failure to use the metric system.

After two months of investigation, the Mars Climate Orbiter Investigation Board released their report, concluding that two different pieces of software aboard the Orbiter used different units of measurement. The measurements used by Lockheed Martin calculated the thrust for orbital insertion with “pound-seconds.” NASA, on the other hand, used “newton-seconds.” The result was that the orbital insertion maneuvers — which should have placed the spacecraft in orbit at an altitude of 110 kilometers — brought it to within 57 kilometers of the surface, where the spacecraft disintegrated, due to atmospheric stress.

This should be a lesson for all engineers, who hopefully will not come within 100 miles kilometers of a similar mishap.